Dimethyl ether (DME) has been studied for a decade as a fuel for portable fuel cell power sources. Chemical intermediates form during the oxidation of DME on a platinum catalyst. These intermediates have been identified using in situ infrared (IR) spectroscopy [1, 2, 3, 4]. Based upon a knowledge of these intermediates, a possible mechanism for DME oxidation on elemental platinum (Pt) has been proposed [5]. This mechanism is summarized in the five following steps below:CH3OCH3+Pt→Pt(C—O—CH3)ad+H++3e  (1)Pt(C—O—CH3)ad+H2O→Pt(HCO)ads+CH3OH  (2)Pt(HCO)ad→Pt(CO)ad+H++e  (3)Pt(HCO)ad+Pt—OH→2Pt+CO2+2H++2e  (4)Pt(CO)ad+Pt—OH→2Pt+CO2+H++e  (5)
Based on an understanding of the above mechanism, bimetallic platinum-based alloys of platinum and ruthenium were found to be effective for oxidation of DME [6]. These bimetallic alloys provide an advantage of being capable of mitigating the poisonous effect of adsorbed CO (i.e. COad) on elemental platinum (Pt).
In a recent study, however, the electrooxidation of DME using the above bimetallic alloys of platinum and ruthenium as electrocatalysts was found to be kinetically handicapped compared to the electrooxidation of methanol using these same bimetallic alloys. If the proposed mechanism shown above is examined closely, step (1) involves the initial adsorption of DME on the catalyst surface, and step (2) involves oxidation of the adsorbed DME by an adsorbed and activated water molecule; step (2) involves splitting a C—O bond. The subsequent steps (3) to (5) are the similar to those that occur during the oxidation of methanol. Without wishing to be bound by any particular explanation, it may be that an activation barrier for the C—O bond cleavage may be responsible for the slower kinetics of DME oxidation compared to the oxidation of methanol.
Transition metals such as palladium (Pd) are known to aid in the C—O bond splitting of ethers [8].
An object of this invention is a composition useful for the catalytic oxidation of dimethyl ether.
Another object of this invention is a process for the catalytic oxidation of dimethyl ether.